A. Field of the Invention
The invention comprises an article handling system, and, more particularly, a wafer handling system. The system includes a transporter for transporting an article from one place to another, a transfer mechanism for removing the article from the track for processing and thereafter returning it for transport, and a loader/unloader for selectively feeding the articles to the track and receiving them therefrom. The system is especially useful in wafer vacuum processing operations.
B. Prior Art
Article handling systems are frequently used in industrial processing operations to minimize manual handling of various articles. In some fields, such as in the processing of semiconductor wafers, the processing is highly automated and numerous handling system of varied characteristics are utilized.
Semiconductor wafers are large, thin, flat wafers (typically, several inches in diameter and several thousandths of an inch thick) which are used in substantial quantities in the semiconductor industry to form electronic circuits and components; they are light in weight (fractions of ounces) and fragile. Successful processing of these wafers requires maintenance of high purity levels in all stages of the operation and much of the processing is therefore performed in a vacuum. One such operation involves selectively irradiating portions of the wafer with an ion beam to thereby modify its electronic characteristic. The irradiation takes place in a vacuum chamber under conditions of moderate to high vacuum (10.sup.-4 torr to 10.sup.-7 torr); the ion beam is admitted to the chamber through a sealed port containing windows that are transparent to the beam.
A wide variety of techniques have heretofore been used to transport the wafers into and out of sealed chambers such as vacuum chambers. Such techniques have included, among others, the use of rotary carousels, endless conveyor belts, movable carriages, etc. With these techniques, the carriage element must at some point penetrate the housing of the chamber, and the penetration points must therefore be sealed so as to isolate the chamber from its ambient environment. Because of the need to accommodate the motion of the carriage element, these seals are of limited effectiveness in sealing the chamber, and thus the vacuum must be reestablished after each wafer is introduced. This is time consuming and often greatly slows production.
In some systems the primary portion of the movable carriage element, together with its driving source, is located wholly within the chamber to help alleviate the seal problem. Special precautions must then be taken to prevent loss of the lubricant element in the driving source, since its loss will subject the driving source to failure and will also contaminate the environment within the chamber. Contamination is an especially serious problem in semiconductor processing.
Because of the stringent requirements placed on the seal and the transport system by the need to maintain high vacuum conditions, therefore, present transport systems, despite their frequently considerable cost and complexity, are only partially effective in maintaining a good vacuum and generally require frequent repair and maintenance.
Once the wafer or other article being processed is moved to the interior of the chamber, it must generally be further handled to position it for processing. For example, in the case of ion beam implantation of semiconductor wafers, the wafer must be held in a position transverse to the beam while the latter scans the wafer. Handling systems to accomplish this frequently are of considerble mechanical complexity, often due in part to the nature of the transport mechanism which carries the wafer into and out of the chamber.
In automated systems, the articles to be processed are often mounted on a carrier; in such cases they must be unloaded from the carrier for processing and returned to it thereafter. Loader/unloader systems to perform this function are frequently complex and often are not well matched mechanically to the transport system.